This is a subject near and dear to my heart as I've had a beowulf at
home for several years now. Amazing as it may seem, it is now entirely
possible to build a beowulf-class cluster at home, and in fact there are
some very useful reasons to think about doing so.

It has become possible for several reasons:

Computers have become almost unbelievably cheap. Very respectably
configured Intel or Athlon based computers are available for as little
as $750 (US) with a graphical head, Windows installed, and some
useless gingerbread. If you can get them to keep Windows and give you
more memory, a bigger disk, and perhaps a nicer monitor you can get a
``head node'' (which doubles as a general purpose desktop) for under
$1000.

Compute nodes, which need be little more than a case with a
processor, some memory, and a network card (no, you don't need even a
floppy disk if you have a PXE/bootp NIC) can cost as little as $500.

Even a fast ethernet switch, which used to be quite costly, is now
available for as little as $100 for 8 ports (quite enough for a small
beowulf).

All the components (running Linux) can serve more than one
purpose. In my house, many nodes are also desktops. In this way I
cover my wife and kids' desktops and also get to use their (mostly
idle) CPUs over the network. Obviously this won't work with any systems
running Windows, unless it is within e.g. VMware.

The most difficult single thing about setting up a home beowulf with
nodes distributed in several rooms is likely to be the physical network.
Houses that are properly wired with category five cabling and RJ45
sockets in all the rooms are relatively rare. However, this is
compensated for by three things.

For one, wireless networks are now relatively cheap. A wireless access
point is less than $200, and a wireless card for a PC or laptop less
than $100. Wireless bandwidth isn't terribly exciting (I tend to get 2
Mbps unless I'm sitting on top of the wireless access point with my
laptop) so you won't be able to run particularly fine grained code, but
wireless is perfectly adequate for coarse grained code and
embarrassingly parallel applications.

For another, having your house wired for a network by professional
electricians isn't horribly expensive, either. Depending on how hard
they have to work, it should cost on the order of $100 per pull from a
reasonable central location (your ``wiring closet'' or wiring shelf,
where you will locate your switch, a small patch panel, and a cable
and/or DSL phone line for external broadband access) to various rooms.
Most of this cost will be labor - it is only a little more expensive to
pull 2-4 cat 5 cables than it is to pull one.

Having four rooms wired (with perhap 12 ports, three per room) and a
terminating patch panel installed might cost around $500 or even less.
It will one day increase the value of your house, and in the meantime it
will make your life better in lots of ways. Go for it.

The final way to proceed is, in the best of beowulf traditions, to Do It
Yourself. The wiring, that is. This is remarkably simple, and cuts out
all the labor costs relative to a professional installation. The
hardware costs are a few hundred dollars for cabling and termination and
tools, and you can install as many lines as you need whereever you need
them.

In my own house (what better testbed?) I have owned and operated a
beowulf for years now. I've even written it up in an article for
;login, complete with pictures19.1. I
used all three of these methods to network my house. I hired
professionals to wire our attic as we had it remodelled into a home
office. I stuck a wireless access point up there (and am working on my
laptop in my living room via wireless as I write these words). I pulled
wires myself into all the downstairs bedrooms, terminating them (and all
the professionally installed wires) in an RJ45 patch panel. I pulled a
category five phone line from our phone service up to the patch panel
for DSL, and a cable up against the possibility that we might one day
use cable instead of DSL (or might want to watch TV on a computer, as
unlikely as that might seem).